Date of Award

Spring 5-1-1992

Document Type

Thesis

Degree Name

Master of Arts (MA)

Department

Geography, Geology, and Anthropology

Abstract

Colorado cyclones have been the subject of many meteorologic and climatologic investigations, but few studies have examined cyclone behavior with a specific focus on a comparison of the spring and fall transition seasons in the upper level westerlies. Periods of change in the number of planetary waves lead to a rearrangement of the longwave pattern in the westerlies and an increased frequency of troughs in the southwestern United States. Short wave disturbances andjor jet maximum moving through the long wave pattern create the potential for Colorado cyclogenetic events and also increasing the frequency of severe weather resultant from these events. In this research, Colorado cyclones occurring in the 30-year period 1961-1990 are analyzed based upon their surface expression. This analysis addresses cyclone location and storm intensity at 12-hour intervals and produces climatic storm tracks and envelopes of occurrence derived from measures of central tendency and dispersion from each time interval. Simple linear regression models are used to link surface cyclone strength and intensity to the 500 mb wind field in which the cyclones are imbedded. Assessment of similarities and differences between the spring season, April and May, and the fall season, October and November were made. Findings indicate that the Colorado cyclones of the spring season occur more frequently than those of fall and have statistically different storm tracks. Intensity, as measured by central pressure and closed circulation, does not appear to be dependent upon transition seasonal differences. Rather these variables may be more strongly related to the month's temporal proximity to winter circulation.

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